Spray drying process



June 17, 1958 A. e. BRENDEL 2,839,133

SPRAY DRYING PROCESS Original Filed July 21. 1949 3 Sheets-Sheet 1 6 5 1Q I 7 f I I I i 27 27 V3 E m I 4 A v N 3 V INVENTOR g 5 mww/v ask/wail.

MW/ KW June 17, 1958 A, G. BRENDEL 2,839,133

SPRAY DRYING PROCESS n ATTORNEY June 17, 1958 A. G, BRENDEL 2,839,133

SPRAY DRYING- PROCESS Original Filed July 21, 1949 3 Sheets-Sheet 3INVENTOR 419mm 6. amps 0x1 BY 1/: aw

ATTORNEY SPRAY DRYING PROCESS 1 Claim. (Cl. 159-48 This inventionrelates to a process for drying solid material dissolved or suspended ina liquid. The principal object of the invention is to provide a methodfor this purpose which will produce a spray dried product of fineparticle size and, if desired, of improved sphericity. A still furtherobject is to provide a spray drying method which can be operated at veryhigh capacity. Another object is the provision of a spray drying methodthat can be carried out in units of large size, with a correspondingreduction in cost per pound of spray dried material. Other objects willbecome apparent from the following detailed cescription of preferredembodiments of the invention when taken with the appended claim.

Although not limited thereto, the process of the invention isparticularly well adapted for the spray drying of slurries containinggelatinous silica, including silicaalumina, silica-magnesia andsilica-alumina-magnesia compositions for use in the catalytic cracl-iingof petroleum hydrocarbons. For this reason the invention will bedescribed in detail with particular reference to the spray drying ofthis class of materials; it being understood, however, that slurries orsolutions of other solid or semisolid material may be dried therein.

In the spray drying of silica slurries for the production ofmicrospheroidal cracking catalysts a two-phase slurry consisting ofwater containing small globules of hydrated silica, silica-alumina,silica-magnesia and the like is dispersed into a current of hot gases ina spray drying chamber. Usually the slurry is dispersed by dischargingit onto a rapidly rotating vaned spray wheel mounted in the top of thedrying chamber. A current of hot gases. such as hot products ofcombustion, is admitted tangentially at the periphery of the chamber andforms a rotating vortex into which the spray of silica slurry isprojected by centrifugal force. In a process of this type theevaporation of the water or other liquid component of the slurry takesplace solely by the sensible heat of the gases, so that these gases arerapidly cooled. The drying capacity of the apparatus is thereforelimited by the amount of heat that can be introduced in the dryinggases.

In accordance with the present invention the spray of material to bedried is subjected to radiant heat as well as to the sensible heat ofthe gases, whereby a number of improvements are obtained. 1 have foundthat by introducing radiant neat into the top of the spray dryingchamber, where the major part of the Water evaporation takes place andthe solid material assumes its final form, a much faster drying rate isachieved. This results in the formation of microspheres of improvedsphericity and smaller average particle size; it also increases thecapacity of the apparatus so that a greater quantity of spray driedmaterial can be produced in an apparatus of any given size per unit oftime. Furthermore, the introduction of radiant heat over the entire topsurface of the spray drying chamber has enabled me to obtain a driedproduct of uniformly small particle size in apparatus of relativelylarge diameter, with a further increase in drying capacity. By soincreasing the diameter of the spray drying chamber, I am enabled toemploy a motor for the spray wheel of more than twice the power of thosethat have previously been used, with a correspond- 2,539,133 PatentedJune 17, 1958 ing increase in the amount of slurry that can be dispersedand spray dried per unit of time.

in addition to the above operating advantages, certain structuraladvantages in the design of the spray drying equipment are also obtainedby the present invention. Principal among these is the simplificationand elimination of duct work that results from mounting the furnace onthe top of the spray drying chamber. While I am not the first to suggestthe location ofa furnace in this position (see U. S. Patent No.1,782,822 to Hechenbleikner), my present construction retains all of theadvantages pointed out in the Hechenbleikner patent and also presentsfurther improvements resulting in the increased drying rate and finerparticle size of the spray dried product noted above.

. The invention will be further described with reference to the specificembodiment thereof shown in the attached drawings in which:

Fig. l is a side view of a spray drier and furnace embodying theinvention with a portion of the furnace shown in section.

Fig. 2 is a vertical section through the furnace and top portion of thespray drier with parts broken away, the section being taken on the line22 of Fig. 3.

Fig. 3 is a horizontal section on the line 3-3 of Fig. 2 with the motorand spray wheel in raised position.

Fig. 4 is an enlarged portion of Fig. 3.

Referring to Figs. 1 and 2 it will be seen that the assembly indicatedgenerally by reference numeral 1 consists of a drying chamber 2 having afurnace 3 superimposed thereon, both being enclosed by a cylindricalside wall 4. Supporting beams 5 carrying a central well structure 6 aremounted on the top of this wall, as by vertical beams 7. The lowerportion of the drying chamber is preferably conical, as at 8, andterminates in a cylindrical outlet 9 containing an eccentrically mounteddeflecting cone 1d surrounded by a duct 11. This duct leads to a set ofcentrifugal separators being connected in turn With an exhaust blowerfor drawing gases through the apparatus. A scrubber irrigated by watersprays may follow the exhaust blower when complete recovery of all ofthe dried material is desired.

As is shown most clearly in Figs. 2 and 3 the furnace 3 is formed withinthe top portion 12 of the side wall 4 by an insulated ceilin 13, whichis suspended from the supporting beams 5 by rods 1 and hangers andimperforate heat-radiating metal partition 16 which ..nstitutes a floorfor the furnace and a horizontal ceiling for the spray drying chamber.This metal partition serves the important function of radiating heatfrom the furnace into the particles of material in the upper portion ofthe spray drying chamber while preventing the uncontrolled admixture ofadditional quantities of hot gases therewith, which increases the dryingcapacity of the apparatus and aids in forming a spray-dried material ofcontrolled shape and particle size.

The partition 16 is made up of a set of metal plates 17 laid on an equalnumber of radial beams 18 which are supported at their outer ends by theside wall 4. At their inner ends 19 these beams are joined as at 29 to avertical annular bafile 21, which is spaced outwardly from the centralwell 6 and forms therewith an annular passage 22. The battle 21 and theinner ends of the beams 19 are supported by a ring of insulated rods 23which extend through the ceiling of the furnace and are hung from thesupporting beams 5. Near its lower edge, and preferably below the levelof the beams t3, the battle is inclined inwardly at 24 to form arestricted portion 25 in which a set of inclined gas-directing vanes 26is mounted.

Set in the outer wall 12 of the furnace are a number of burner tunnels27, each enclosing a gas burner 28.

, that'this How soon becomes very hot and radiates a V substantialproportion of the heat from the burners directly into the drying spacebelow with a corresponding reduction in the burner gas'temperatures. Thepartiallyv cooled products 'of'combustion, at the end of their spiralpath around the furnace,,pass upwardly over the vertical 7 bafiie 21 anddownwardly through the spaces 22 and 25 attemperatures of about 600 to1400 F. and preferably at about1400 F., being deflected by the vanes 26into 'a vertically rotating path.

Under some conditions of operation it may be advisable to admit hotgases fromthe furnace 3 to the peripheral portion of the drying chamber2. In order to accomplish this. purpose a set of supplementary gaspassages 31 is provided in the partition 16. Each of these passages isfitted'with a connecting pipe 32 containing a damper 33 operating on arod 34 that extends through the outer wall of the spray drying chamber,so that the damper can be opened, closed or adjusted from outside as isshown in Fig. 4 of the drawings. By suitable operation of these dampersthe possibility of a dead air space in V the outer-upper portions of thespray drying chamber is avoided. a

As has been stated, the drying capacity of the apparatus of the presentinvention is, such that a spray machine can be used having a greaterpower output thanany' heretofore employed for this purpose. Such amachine is shown at 35 on Fig. 2 of the drawings.

The spray machine 35 is adapted to fit closely within a verticalcylinder 80 in the central well structure 6,

and is provided with an outer flange 81 which rests on an inner'shoulder82 in the cylinder 80 when the motor and spray Wheel are in operativeposition. The central cylinder 80 is braced against vibration by a setof brackets 83 which'span the annular space 84 between the'innercylinder 80 and the outer,'insulated cylinder 85 of the centralwellstructure 6. It will thus be seen that the spray machine is protectedfrom the heat of the furnace, first by a layer of insulation 86 on theinner wall of the furnace and then by the air space 8 e V The advantagesof my process are best shown by a specific example of results which havebeen obtained herein. A slurry. of a hydrated silica-alumina catalyst,containing 87% of silica and 13% of alumina on the dry basis andprepared by suspending in water a precipitated, filtered and washedsilica-alumina produced as described in the patent of K. D. Ashley andA. O. Iae er,

No. 2,478,519 dated August 9, 1949, was supplied at a used as fuel inthe furnace 3, which furnace contained 6 gas burners each having acapacity of 6,000,000 B. t. u.

per hour. The gas flow was estimated at 2380 lbs. per

minute, based on the heat balance and the air-to-gas ratio was adjustedto maintain temperatures of l600-1800 F.

at the burner tunnels 27. The outlet gas temperature in the pipe 11 was250 F. The following operating results were obtained when a 9-inchdiameter, 45 j-type spray wheel was used.

Atornlzing Speed, R. P. M 10,700 10,700 r 12,700 10,700 12,700

Side Inlet Dampers33 open closed open open closed Gas Temp. F.) inPassage 710 750 640 640 600 Screen Analysis:

40 mesh, percent 100 100 100 100 100 100 mesh percent- 95 97 99 99 100200 n'esh percent. 62 71 84 73 85 -40 microns, percen 28 31 40 30 43 -20microns, percent 6 6 8 7 9 10 microns, percent. 7 0 0 0 V 0 2 WaterContent of Product,

Percent 13 14 13 12 12 From the foregoing it will be seen that theessential features of'my invention consist in the steps of discharginghot combustion gases across one or more surfaces of aheat-radiatingmetal partitionan opposite side of which is so positionedas to radiate heat into the drying chamber, thereby partially coolingthe hot gases by transmitting their excess heat directly to the spraydrying operation,

followed by projecting the material to' be driedinto the partiallycooled gases. .These. principles can be embodied in a variety of typesof equipment other than' that which has been specifically described.Thus, for example, the natural gas or other fuel maybe burned injuxtaposition to one or rnore vertical heat-radiating partitionssurrounding the upper part of the spraydrying chamber at temperatures of1600 -2300 F. and the resulting hot gases may then be passed over thepartition 16 and down through the central gas passage25.

/ Another embodiment could employ a ring of heat-radiating tubes, closedat their lower ends and suspended from the central areas of the plates17 and projecting down:

wardly into the upper portion of the spray drying chamber, these tubeshaving gas 1 burners positioned therein, whereby a'large proportion ofthe heat of combustion would be radiated directly into the spray dryingchamber. In this case the partially cooled gases leaving the open upperends of the combustion tubes would likewise pass over the partition'16and downwardly through. the central orifice '25 after which the materialto be' spray, dried would be injected therein. These and other types ofapparatus suitable for practicing the invention will be evident to thoseskilled in the art from the foregoing description. 7

This is a division of my copending application Serial 'No. 105,943 filedJuly 21, 1949'now U. S. Patent No.

2,644,516 issued July 7, 1953. V

Whatlclaimis: f A method of spray drying an aqueous two-phase slurrycomposed of water containing small globules of a hydrated siliceous gelwhich comprises generating hot gases having a temperature of about16002300 F. by

burning fuel in juxtaposition to the outer edge of the upper surface ofa horizontal metal partition having a centrally located outlet thereinand passing them thereacross in a spiral path to' said centrally locatedoutlet, thereby simultaneously heating said partition uniformly toheat-radiating temperatures and partially cooling said gases to about600l400 F., passing the partially cooled gases downwardly through saidoutlet while simultaneslurry and converting the silica to a hardenedgel.

References Cited in the file of this patent UNITED STATES PATENTS1,648,937 .Dickerson Nov; 15,1927 1,711,306 Bowen' Apr. 30, 19291,713,237 7 Morin May, 14, 1929 1,722,175 Bowen July 23,1929 1,778,310Covlling et al Oct. 14,1930 1,779,296 Spross Oct. 21, 1930 1,782,822Hechenbleikner Nov. 25, 1930 1,875,755 Noyes Sept. .6, 1932 2,396,689Davis Mar. 19,1946 2,473,035 Meade et al. June 14, 19.49 2,478,779Piepcr Q. Aug, 9, 1949 2,506,646 'Komline May 9, 1950 2,562,473Mojonnier July 31, 1951' 2,584,973 Andermatt Feb. 12, 1952 19532,644,516 Brendel July 7,

